1. Field of the Invention
The invention relates to connecting rods. More particularly it relates to connecting rods used in internal combustion engines and compressors to connect a crankshaft to a piston.
2. Description of the Art
In conventional internal combustion engines, connecting rods transmit the reciprocating motion of the pistons to the crankshaft and thereby convert it to rotary motion. For ease of assembly, the rod is usually formed with a main shank that has a top bore for receiving a piston connector and a lower part that partially surrounds the crankshaft. The rod also has a cap which extends the rest of the way around the crankshaft. The cap and shank are bolted together to sandwich the crankshaft.
Connecting rods are subject to stress, shock and temperature (and thus wear) as they rapidly change from being compressed to being tensed. Moreover, it is highly desirable to make the connecting rods as light as possible. This has lead to the use of aluminum, other lightweight metals and even plastic. However, the use of these materials creates other design problems. In particular, it is generally necessary to use steel bolts to connect the shank part of the connecting rod with the cap part. When two bolts are used for this purpose, the difference between the thermal coefficients of expansion of the steel bolt and the aluminum rod tends to cause wear and reduced efficiency.
In order to reduce the problem of uneven thermal expansion, as well as to reduce weight and assembly and repair costs, connecting rods employing only one bolt have been used. Many of these use a bolt extending crosswise through legs located either on the rod's shank or cap, either above or below the crankpin opening. See U.S. Pat. Nos. 491,727; 678,021; 1,009,244; 1,130,982; 1,253,841; 3,576,353; 4,541,304; and 4,836,044. In these rods, the bolt is subject to substantial shearing forces, may not effectively maintain a round crankpin opening and may require additional parts to properly align the crankpin opening.
Some others have employed a bolt generally in line with the longitudinal axis of the connecting rod, but these have also used additional parts to maintain alignment and rounding of the crankpin opening and in many cases have employed opposite the bolt a hinged junction, a complexity which increases the cost of manufacturing and can cause reliability problems. See U.S. Pat. Nos. 1,226,603 and 1,786,934.
There remains a need for a single bolt connecting rod in which the bolt is oriented so that substantial shear forces are avoided, and which eliminates the need for a separate part to cause correct alignment of the crankpin opening.
In small engines the connecting rod shank is often flared wider near the interface with the cap in order to provide separation from adjoining shanks or crankshaft arms. Flaring the shank is difficult in an extrusion or fine blanking process. Thus, there is a need to provide separation while allowing the shank to be of a uniform width.
Another problem is that connecting rods are generally made in a relatively expensive die-casting process. Parts so produced usually require additional machining to achieve required tolerances. In addition, some percentage of the rods produced by the die-cast process are unusable because of excess porosity. The die-cast process therefore entails substantial labor, inspection, and scrapping costs.
Accordingly, there is a need to reduce the costs of manufacturing, installing and repairing connecting rods. A further need is to provide a lightweight connecting rod with good wear characteristics. A further need is to find a way to eliminate the use of connecting rod spacers.